The present invention relates, in general, to tamper-evident closures of the type described in U.S. Pat. No. 4,526,282, and in U.S. Pat. No. 4,552,328, both assigned to the assignee hereof. More particularly, the present invention is an improvement over the cap assembly disclosed in the aforesaid patents, and provides a structure which is more easily removed from the mold in which it is formed, and which is more easily applied to threaded containers without damage to the tamper-evident skirt.
Tamper-evident closure caps for containers are well-known, and are increasingly in demand for a wide variety of applications. A recurring problem in the production of such caps is the difficulty in making them sufficiently strong that they can be removed from a mold intact, and will remain intact during handling, shipment, and application to a container, yet still be sufficiently weakened where the tamper-evident skirt portion is attached to the cap that the skirt portion will always tear away from the cap whenever the cap is removed from its container. This problem has led to a wide variety of cap designs, has led to a variety of techniques for applying the caps to the container so as to compensate for design flaws dictated by manufacturing considerations, and has led to the design of complex mold configurations to enable the caps to be removed intact from the molds after they are formed. Such difficulties have adversely affected the cost of manufacturing such caps, particularly when they are made of plastic or other synthetic materials. Thus, in some cases the caps must be cut and heated after the molding step, the cutting being done to produce a weakened area between the cap and depending security ring, and the heating being done to deform the security ring onto the container. In other cases, the prior art suggests that the removal of a molded cap from its mold cavity can be facilitated by connecting the lower tamper-evident skirt to the upper cap portion in such a way that the inside diameter of the skirt is equal to the outside diameter of the cap. Although this does allow easy removal of the device from the mold, it also serves to increase the size of the mold and further requires a deformation step after the cap is placed on a container to ensure that the security ring engages the container. It has also been proposed to form the weakened area between the tamper-evident skirt and the cap by producing an annular V-shaped groove. However, the molding of such a cap requires a tool having complex cams and angle pins which increase the complexity and thus the cost of the mold. All of the foregoing factors adversely affect the cost of manufacturing closure caps with tamper-evident skirts, and applying such caps to containers.
Because manufacturing techniques impose restrictions on the shape of a cap, it is desirable to provide a tamper-evident closure cap design which is cost effective from the manufacturing standpoint. This involves a cap design which is easy to apply to a container and which is also effective to provide evidence of cap removal, while at the same time permitting a tool design which would be relatively simple and inexpensive, consistent with reliable manufacture of the cap. Easy application of the closure to a container is essential if costs are to be reduced, and if damage to the caps is to be avoided. Thus, it is desirable to avoid the cutting and heat-shrinking methods which have been used in prior devices, but to do this, it is necessary to provide a cap having a tamper-evident skirt that is of the final desired size. This has been a problem with prior designs, since in placing the cap on a container, the skirt portion must expand to allow it to fit over the container finish threads and the tamper-evident retainer bead. Preferably, such caps are merely pressed onto the container, although that may be threaded on, with the tamper-evident skirt portion snapping over the tamper bead on the container without damaging the skirt portion. With prior designs, expansion of the skirt portion has often led to its fracturing, rendering the cap unusable, or has caused the skirt portion to stretch out of shape, requiring heating to return it to its initial size. Occasionally, the skirt catches on the container threads during application, and folds under, rather than expanding, thus ruining the cap. Sometimes the pressure required to seat the cap on the container will fracture the connectors which fasten the skirt to the cap, so the cap becomes unusable.
It is, therefore, desirable to provide a tamper-evident closure cap which is capable of being applied to a container over the finish threads and tamper-evident bead to provide a tamper-evident closure without the need for additional application steps and without the danger of fracturing the tamper-evident skirt portion.